1. Field of the Invention
The present invention relates to a process for manufacturing an optical recording medium which optically records digital information, including a write-once optical recording medium on which a user can write information only once, and an erasable optical recording medium on which information can be repeatedly written and erased.
2. Description of the Related Art
The present inventors have already disclosed optical recording mediums using a recording layer which takes two stable crystalline states exhibiting different optical characteristics transformed by an irradiation of light pulses having different powers and irradiation times in Japanese Unexamined Patent Publication (JUPP) (Kokai) No. 61-134944 published on June 23, 1986; JUPP No. 61-168145 published on July 29, 1986; and, JUPP No. 61-168144 published on July 29, 1986, among others. These recording mediums are provided with a recording layer having a uniform chemical composition in the direction of the layer thickness and are manufactured by depositing a layer having the chemical composition on a substrate while heating the substrate or by depositing such a layer followed by scanning tracks of the deposited layer with a laser beam, so that the deposited layer, or only the tracks of the deposited layer, are crystallized.
However, these processes are disadvantageous in that they require a long time for heating and cooling a substrate or for scanning a laser beam, and further, require a substrate having a high heat-resisting feature. Moreover, in the above processes, the reflectivities of a recording layer can not be altered over a wide range by selecting a thickness of the recording layer, since the recording layer has a uniform chemical composition.
The inventors developed another process for manufacturing such an optical recording medium, which comprises depositing a plurality of layers followed by heating the layers to form a recording layer (see Japanese Unexamined Patent Publication (Kokai) No. 62-20,154, published on Jan. 28, 1987). However, this process also requires a long manufacturing time, and has a disadvantage in that the characteristics of the resultant recording medium are inferior.